Perform basic validation on K3S_URL in install.sh
Perform basic validation on K3S_URL in install.sh

This allows us to fail quickly if we're handed a schemeless or plain
HTTP URI, rather than having the agent barf when the systemd unit
starts. For an operator, this makes for a cleaner error up front and
clear messaging for how to fix the situation.

Signed-off-by: Josh McSavaney <3582ab6848926274f6941ff1847cdb8bd6b84e54@csh.rit.edu>

rancher/k3s,rancher/k3s